AQA GCSE Chemistry Chemistry Paper 1 (Foundation), June 2022: Question 4

✅ Correct Answers

• 04.1 [1 mark]: For elements that had not been discovered (at that time) OR so elements with similar properties were grouped together. (Also accepts: "for missing elements").
• 04.2 [1 mark]: Mendeleev
• 04.3 [1 mark]: Noble gases

💡 Key Knowledge

• Dmitri Mendeleev arranged elements primarily by atomic weight but swapped order where chemical properties didn't match.
• Crucially, he left gaps and predicted properties of undiscovered elements (e.g. gallium, germanium).
• Group 0 (the noble gases) were unreactive gases and completely undiscovered when Mendeleev made his 1869 table.

❌ Common Errors

• 04.1: Saying gaps were left "for atomic numbers" or "due to atomic mass" — atomic number (protons) was not known until decades later!
• 04.2: Confusing Mendeleev with Bohr (electron shells) or Chadwick (neutron discovery).

🧠 Exam Technique

Always use the exact historical term: gaps were left for undiscovered elements. Notice in Figure 6 that helium, neon, and argon are missing on the far right—identifying this instantly gives you Group 0 (noble gases) for 04.3.

✅ Correct Answers

• 04.4 [1 mark]: The elements all have one electron in the outer shell.
• 04.5 [1 mark]: Any value in the range 49 to 88 (°C) (e.g. 63 °C).

📐 Trend Analysis (04.5)

Table 3 shows a clear decreasing trend in melting point down Group 1:

• Na (98 °C) is 83 °C lower than Li (181 °C).
• Potassium (X) must fall between Sodium (98 °C) and Rubidium (39 °C).
• Midpoint estimate: (98 + 39) / 2 = 68.5 °C. The accepted range is very generous: 49 °C to 88 °C.

💡 Key Knowledge

Group number = number of outer shell electrons. Chemical reactions involve losing, gaining, or sharing these outer electrons. Because all Group 1 atoms have 1 outer electron, they all react similarly by losing that 1 electron to form 1+ ions.

❌ Common Errors

• Selecting "elements all have the same number of shells" (shells increase going down the group).
• Selecting "elements all form negative ions" (metals form positive ions/cations).
• Giving an estimated melting point outside 49–88 °C, such as numbers above 98 °C or below 39 °C.

✅ Correct Answers

Give any one of the following [1 mark]:

• Floats (or moves on the surface)
• Melts (or forms a molten ball / sphere)
• Fizzes / bubbles / effervescence / gas given off
• Catches fire / produces a flame (lilac flame)
• Accepts: explodes / disappears

❌ What Examiners Do NOT Accept

• Heat/temperature changes: "It gets hot" is not an observation you see without a thermometer.
• Sounds: "A popping noise" or "hissing" (examiners ignore sound references for visual observation questions unless specified).
• Naming products: "Hydrogen gas is made" is an inference, not a direct observation (write "bubbles" instead).

✅ Correct Answers

• 04.7 - State of Chlorine at 150 °C [1 mark]: gas
• 04.7 - Formula of Astatine with Hydrogen [1 mark]: HAt (capital H, capital A, lowercase t)
• 04.8 - Formula of a Bromine Molecule [1 mark]: Br₂

💡 Pattern Spotting in Table 4

• State of Chlorine: Chlorine boils at -34 °C (a gas at room temperature). Therefore, at 150 °C it is definitely a gas. Notice fluorine and bromine are already gases at 150 °C, so chlorine must be too.
• Formula with Hydrogen: Look at the 1:1 ratio pattern: HF , HCl , HBr , HI → following this trend, astatine forms HAt .
• Diatomic Halogens: Halogens exist as pairs of atoms bonded covalently: F₂ , Cl₂ , Br₂ , I₂ .

🧠 Exam Technique: Subscripts vs Superscripts

In question 04.8, pay very close attention to formatting:

• Br₂ (subscript 2) means 2 atoms covalently bonded in one molecule → CORRECT.
• Br² (superscript 2) is a mathematical power → INCORRECT.
• 2Br means two separate unbonded bromine atoms → INCORRECT.

❌ Common Errors in 04.7

• Writing liquid for chlorine by incorrectly applying room temperature states.
• Writing incorrect casing for astatine hydride, such as HAT or hat instead of HAt .